This application concerns capillarity, also referred to as capillary action or capillary force. In a particular embodiment, the invention concerns an assay device that comprises multiple capillary force-inducing surfaces having distinct positional orientations.
With the advent of field-based testing and point of care testing in hospitals, it has become increasingly important to develop diagnostic products which are simple, rapid and convenient for use. In these contexts, results are generally needed rapidly, with a minimum of time given to the performance of a test. Providing an assay result in minutes allows prompt action to be taken in a hospital or field setting.
Field-based testing (i.e., a non-laboratory setting) has become increasingly common. Such non-laboratory settings include, e.g., environmental testing for contaminants, testing in workplaces, and testing in sports medicine at an activity site. Testing in non-laboratory settings may often be performed by individuals who have minimal training in the conducting of assays, or those who do not regularly conduct assays. Additionally, non-laboratory settings often lack the same level of access to assay equipment or reagents found in laboratories. Thus, it would be advantageous to have an assay device for use in a non-laboratory setting that is simple to use, and where the device does not necessitate laboratory equipment beyond the assay device itself; such devices are also advantageous in hospital/laboratory settings.
Point of care and non-laboratory testing is facilitated by compact small devices which are convenient to transport and use. Preferably the design is easily manipulated by the individual performing the assay. It is also preferable that the assay device be capable of being fed into hand-held instrument that provides a determination (qualitative or quantitative) of the assay result. Devices capable of being fed into hand-held instruments (such as a reader) are preferably compact and have a flattened configuration.
Preferably a device for use in point of care or non-laboratory settings does not require any additional equipment to affect an assay. This feature makes the device easier to use and avoids the need to purchase or use any additional equipment. For example, it is preferred that such a device does not require externally applied pressure.
Capillary force has been used to achieve movement in assay devices without externally applied pressure. To achieve such movement, e.g., assay material is placed in a proximal location in the device, a location that contains a base level of capillary force. One or more distal regions contain surfaces that induce comparable or greater capillary force than the base level at the proximal location. If more than one distal region contains surfaces that induce capillary force, the effective amount of capillary force induced is successively greater at each distal region, or is comparable in all regions so that there is proximal to distal movement of fluid through the device.
A problem with the use of capillarity as a means to achieve proximal-to-distal movement through a device concerns the fluid volume required to perform an assay, i.e., the xe2x80x9cassay volume.xe2x80x9d An assay result is often achieved only when the sample has traveled through the device. In some cases, e.g., when bound label is used as a means of detection of an analyte, an assay result is only achieved when the unbound label is removed from the zone in which the bound label is detected. Moreover, if multiple reactants must be added to the device, the distal region of the device must accommodate sufficient volume for the sample and all reactant fluids. However, in order to achieve sufficient distal capillarity in a compact device, dimensions in the distal areas are often extremely minute. Moreover, minute dimensions are often desired in assay devices to improve reaction kinetics, by minimizing diffusion distances for the assay reagents.
If sample and non-sample fluids must be accommodated distally, devices with sufficient capillarity and the requisite capacity have highly impractical configurations for laboratory or field settings. If a capillary in a distal region is made larger to accommodate an assay volume (a reaction volume and other needed volumes), the drop in capillarity in that region often impairs fluid flow into the region.
Accordingly, there is a need for an efficient, compact, economical device that permits the assay result to be readily determined. It is also preferable that the device not necessitate additional assay equipment in order for an assay to be performed.